1. Field of the invention
The invention relates to an iron sponge briquetting press having two opposite rollers provided with cooling ducts, each roller comprising a roller base body and a coating affixed thereto with moulding recesses for shaping the briquettes in a nip formed by both rollers.
2. Description of the Prior Art
Iron sponge is an ore, where the nonferrous components are removed so that subsequently a spongy structure with a very high pore volume is left over. This iron sponge is briquetted at temperatures of about 700.degree. C., before it is further processed in furnaces. The material to be briquetted consists substantially of iron oxide and gangue material, i.e. minerals leading to a heavy wear of the roller coating. The iron sponge to be briquetted can be shaped relatively well due substantially to the high processing temperature of about 700.degree. C.; however, the minerals remaining in the iron sponge nevertheless cause heavy wear.
Therefore briquetting presses have been used for the briquetting of iron sponge for about 20 years, said presses having coating comprising an especially hard, wear-resistant material. This material is designated as M3 according to the US Standard and S653 (steel code 1.3344) according to the DIN Standard. This material provides for relatively hard and wear-resistant surfaces of the coating and the moulding recesses formed therein.
Ring segments were produced from this material which were tightened on the roller base body via laterally engaging clamping rings. Segments were not only used for the coating, because the material is too brittle so that it cannot be processed in greater dimensions, but also due to the high differences in temperature and the heat expansion and shrinking of the coating of the rollers connected therewith. Despite the relatively high specific pressing force of the rollers which is at 120 to 140 kN/cm (width of the nip), the segment service lives are relatively long. However, damage due to local, punctiform overloads occur again and again, which are caused by foreign bodies contained in the iron sponge. It would be possible per se to exchange only individual segments in case of such damage. However, this exchange is only possible if the exchange segment has the same wear condition. Since such segments are only rarely available as an individual segment, an entire set of segments must mostly be exchanged. This reduces the average service life of the segments and leads above all to unplanned standstills.
Apart from the fact that the production of the coating used so far is difficult due to the material used, the coatings are also expensive.
Therefore it is the object of the present invention to improve an iron sponge briquetting press so that the roller coatings are less expensive, more easily to process and less sensitive to local overloads.